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Topic: Nuclear fission

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In the News (Wed 20 Mar 19)

  Nuclear fission - Wikipedia, the free encyclopedia
Fission is useful as a power source because some materials, called nuclear fuels, both generate neutrons as part of the fission process and also undergo triggered fission when impacted by a free neutron.
Nuclear fuels can be part of a self-sustaining chain reaction that releases energy at a controlled rate in a nuclear reactor or a very rapid uncontrolled rate in a nuclear weapon.
Nuclear fission differs from other forms of radioactive decay in that it can be harnessed and controlled via a chain reaction: free neutrons released by each fission event can trigger yet more events, which in turn release more neutrons and cause more fissions.
en.wikipedia.org /wiki/Nuclear_fission   (2538 words)

 Nuclear weapon - Wikipedia, the free encyclopedia
In fission weapons, a mass of fissile material (enriched uranium or plutonium) is rapidly assembled into a critical mass, in which a chain reaction begins and grows exponentially, releasing tremendous amounts of energy.
Nuclear weapons were symbols of military and national power, and nuclear testing was often used both to test new designs as well as to send political messages.
Nuclear weapons have been at the heart of many national and international political disputes, and have played a major part in popular culture since their dramatic public debut in the 1940s, and have usually symbolized the ultimate ability of mankind to utilize the strength of nature for destruction.
en.wikipedia.org /wiki/Nuclear_weapon   (2384 words)

 Kids.net.au - Encyclopedia Nuclear fission -   (Site not responding. Last check: 2007-10-21)
In physics, fission is a nuclear process in which a heavier unstable nucleus divides or splits into two or more lighter nuclei, with the release of substantial amounts of energy.
The principle of operation of both nuclear weapons and nuclear reactors is that a nuclear chain reaction must occur.
At the meeting Bohr and Fermi discussed the problem of fission, and in particular Fermi mentioned the possibility that neutrons might be emitted during the process.
www.kidsseek.com /encyclopedia-wiki/nu/Nuclear_fission   (2777 words)

 Nuclear fission - Wikipedia, the free encyclopedia   (Site not responding. Last check: 2007-10-21)
Fission can be induced by several methods, including bombarding the nucleus of a fissile atom with another particle of the correct energy.
Though fission is most often and most easily initiated by the absorption of a free neutron, it can also be induced by striking a fissionable nucleus with other particles.
This situation (expected number of neutrons causing fission is one or more) is called criticality, and the configuration is called a critical mass (although strictly speaking the shape is as important a factor as the mass; see below).
www.berkeley.biz /project/wikipedia/index.php/Nuclear_fission   (2975 words)

 nuclear fission
Nuclear fission was discovered in 1938 by Otto Hahn and Fritz Strassmann while attempting to produce elements heavier than uranium by bombarding uranium with neutrons.
It was established that nuclear fission occurs when a particle such as a neutron strikes the nucleus of a uranium atom and causes it to split into two fission fragments, each of which is composed of a nucleus with roughly half the neutrons and protons of the original nucleus.
Nuclear fission is one of three types of nuclear reactions that release substantial amounts of energy, the other two being radioactive decay and nuclear fusion.
www.britannica.com /nobel/micro/431_68.html   (512 words)

 nuclear fission - Hutchinson encyclopedia article about nuclear fission
It is accompanied by the emission of two or three neutrons and the release of large amounts of nuclear energy.
Fission occurs spontaneously in nuclei of uranium-235, the main fuel used in nuclear reactors.
The neutrons released spontaneously by the fission of uranium nuclei may therefore be used in turn to induce further fissions, setting up a chain reaction that must be controlled if it is not to result in a nuclear explosion.
encyclopedia.farlex.com /nuclear+fission   (264 words)

 Nuclear Fission Propulsion - Future Space Propulsion Systems (Future of Space Exploration)
Nuclear fission is the splitting of an atom into several smaller fragments.
The fissionable atom then captures the neutron and splits (decays) into two smaller atoms (isotopes such as iodine-131, caesium-137 and strontium 90) and two or three neutrons, which go on to split other fissionable nuclei resulting in a chain reaction.
Nuclear fission produces highly energetic fragments and this system uses these fragments as the propellant fluid by allowing them to escape the reactor.
www.thespacesite.com /space/future/fission.php   (1075 words)

 World Nuclear Association | Education | Some Physics of Uranium
Whether fission takes place, and indeed whether capture occurs at all, depends on the velocity of the passing neutron and on the particular heavy nucleus involved.
It is nonetheless possible to use this so-called fast fission in a fast reactor whose design minimises the moderation of the high-energy neutrons produced in the fission process.
Creation of the fission fragments is followed almost instantaneously by emission of a number of neutrons (typically 2 or 3, average 2.5), which enable the chain reaction to be sustained.
www.world-nuclear.org /education/phys.htm   (3824 words)

 Fission and Fusion   (Site not responding. Last check: 2007-10-21)
Nuclear energy is contained within the center of the atom in a place known as the nucleus.
In the fission process certain heavy elements, such as some forms of Uranium, are split when a neutron strikes them.
Fission is a nuclear reaction in which an atomic nucleus splits, or fissions, into fragments, usually two fragments of comparable mass, with the release of large amounts of energy in the form of heat and radiation.
reactor.engr.wisc.edu /fission.htm   (443 words)

 The Difficult Years: Fission Research, 1939 - 1945
Nuclear fission involved the splitting of nuclei with the release of enormous amounts of energy.
The frightening possibility that this German effort might succeed in providing Hitler with a nuclear weapon was one of the driving forces of the Manhattan Project in the United States, which produced the nuclear weapons dropped on Japan in August 1945.
The fate of nuclear work was sealed by the military's eventual decision not to give it generous support, but to concentrate on rockets and jet aircraft.
www.aip.org /history/heisenberg/p11.htm   (1107 words)

 World Nuclear Association | Information and Issue Briefs | Glossary
Fission: The splitting of a heavy nucleus into two, accompanied by the release of a relatively large amount of energy and usually one or more neutrons.
Nuclear reactor: A device in which a nuclear fission chain reaction occurs under controlled conditions so that the heat yield can be harnessed or the neutron beams utilised.
Thermal reactor: A reactor in which the fission chain reaction is sustained primarily by slow neutrons, and hence requiring a moderator (as distinct from Fast Neutron Reactor).
www.world-nuclear.org /info/inf51.htm   (2718 words)

 Nuclear Fission Energy
The energy released in the fission process, which is primarily in the form of the kinetic energy of the fission fragments, heats the water.
The smaller fission cross sections associated with the fast neutrons (as compared with thermal neutrons) leads to higher fuel concentrations in the core and higher power densities, which, in turn, create significant heat transfer problems.
Nuclear fission reactors, usually pressurized water reactors with energy conversion based on a steam-turbine cycle, have been used extensively to power ships.
www.lbl.gov /abc/wallchart/chapters/14/1.html   (1302 words)

 Nuclear Energy is the most certain future source.   (Site not responding. Last check: 2007-10-21)
This page discusses nuclear energy as a part of a more general discussion of why human material progress is sustainable and should be sustained.
The basic energy fact is that the fission of an atom of uranium produces 10 million times the energy produced by the combustion of an atom of carbon from coal.
A nuclear reactor engine that would provide the right amount of energy for a car could be built and would run fine and would require refuelling only every 5 or 10 years.
www-formal.stanford.edu /jmc/progress/nuclear-faq.html   (5211 words)

 (S-8) Nuclear Energy
The nuclear forces apparently prefer equal numbers of each kind, and light nuclei--helium, carbon, nitrogen, oxygen--usually maintain a 50:50 ratio, although nuclear variants ("isotopes";) with small deviations from equality may exist and may be stable.
It has been proposed to cast nuclear waste into a glassy slag and isolate it in underground caverns, but fears remain--no human activity in past history has required such an unfailing long-term commitment (toxic chemicals also may do so, if they are buried instead of destroyed).
However, nuclear waste is still kept in temporary storage, as the national policy for its treatment and disposal continues to be debated.
www.phy6.org /stargaze/Snuclear.htm   (3266 words)

 Nuclear Fission
If a massive nucleus like uranium-235 breaks apart (fissions), then there will be a net yield of energy because the sum of the masses of the fragments will be less than the mass of the uranium nucleus.
The fission of U-235 in reactors is triggered by the absorption of a low energy neutron, often termed a "slow neutron" or a "thermal neutron".
Plutonium-239 is also fissionable by bombardment with slow neutrons, and both it and uranium-235 have been used to make nuclear fission bombs.
hyperphysics.phy-astr.gsu.edu /hbase/nucene/fission.html   (592 words)

 nuclear energy: Nuclear Fission
The process of nuclear fission was discovered in 1938 by Otto Hahn and Fritz Strassmann and was explained in early 1939 by Lise Meitner and Otto Frisch.
The average energy released by the fission of uranium-235 is 200 million electron volts, and that released by uranium-233 and plutonium-239 is comparable.
Fission can also occur spontaneously, but the time required for a heavy nucleus to decay spontaneously by fission (10 million billion years in the case of uranium-238) is so long that induced fission by thermal neutrons is the only practical application of nuclear fission.
www.factmonster.com /ce6/sci/A0860068.html   (413 words)

 Nuclear fission - LearnThis.Info Enclyclopedia   (Site not responding. Last check: 2007-10-21)
When a free neutron of the proper energy is absorbed by the nucleus of a fissionable atom, the resulting unstable nucleus will split producing two or more fission products, two or three free neutrons and a tremendous amount of energy compared to chemical reactions.
The fission products are atomic nuclei of different elements formed from the protons and neutrons originally comprising the nucleus before its fission.
These fission products are highly radioactive and become the waste of nuclear energy production.
encyclopedia.learnthis.info /n/nu/nuclear_fission.html   (2834 words)

 Nuclear Chemistry and the Community
You may remember that the transformations we see in the world; the burning of fuels, the growth of plants, the rusting of iron, are all results of the movement of electrons with a negative charge, that are the source of the making and breaking of chemical bonds.
Nuclear Energy for Power and Weapons: The energy released by fission excited the European scientists who discovered the phenomenon.
In the "fuel rods", as the uranium is fissioned and the energy is drawn from the fission reaction, some neutrons react with the bulk of the uranium, the nonfissionable
www.chemcases.com /nuclear   (1058 words)

 Nuclear Weapon Design
Nuclear weaponry has advanced considerably since 1945, as can be seen at an unclassified level by comparing the size and weight of “Fat Man” with the far smaller, lighter, and more powerful weapons carried by modern ballistic missiles.
The minimum mass of fissile material that can sustain a nuclear chain reaction is called a critical mass and depends on the density, shape, and type of fissile material, as well as the effectiveness of any surrounding material (called a reflector or tamper) at reflecting neutrons back into the fissioning mass.
Nuclear weapons are particularly destructive, with immediate effects including blast and thermal radiation and delayed effects produced by ionizing radiation, neutrons, and radioactive fallout.
www.fas.org /nuke/intro/nuke/design.htm   (3646 words)

 Nuclear Chemistry - Nuclear Fission
They quickly understood that fission would create a large amount of energy, and balanced nuclear equations indicated additional neutrons would be produced.
In the latter case, the secondary neutrons may be used to produce new fissions and if a sufficient number of fissions occur, they will produce enough neutrons to sustain a chain reaction.
Until this discovery, the lighter isotope was not considered of importance in nuclear reactions because of its low concentration.
www.chemcases.com /nuclear/nc-03.htm   (1170 words)

 Invention and Discovery: Atomic Bombs and Fission
It would be logical to assume that the discovery of fission preceded the invention of the atomic bomb.
Later, when the possibility of a German atomic bomb had been shown to be nonexistent, Szilard campaigned vigorously against the use of the bomb, and went on to help found The Bulletin of Atomic Scientists and The Council for a Livable World.
By mid January Szilard heard about the discovery of fission from Eugene Wigner, and immediately realized that the fission fragments, due to their lower atomic weights, would have excess neutrons which must be shed.
nuclearweaponarchive.org /Usa/Med/Discfiss.html   (1259 words)

 fission, nuclear
A chain reaction results when the neutrons released during fission cause other nearby nuclei to break apart.
Fission may occur spontaneously or may be induced by capture of bombarding particles.
In addition to the fission fragments, neutrons and gamma rays are usually produced during fission.
www.daviddarling.info /encyclopedia/F/fissionnuc.html   (148 words)

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